They have changed the downtime to 7 hours as per this post below from official blog.

Hello!
We have just received word that maintenance will now be taking longer than what we had originally posted on Friday.

We will now be performing scheduled maintenance for seven hours on Tuesday, April 3rd, 2012 from 2AM CDT (12AM PDT/3AM EDT/8AM BST/9AM CEST/5PM AEST) until 9AM CDT (7AM PDT/10AM EDT/3PM BST/4PM CEST/12AM AEST). All game servers and SWTOR.com will be offline during this period. This maintenance is expected to take no more than seven hours, but could be extended.
Also 8am BST is British summer time so GMT/UTC is -1 hour. They had the wrong time zones apparently and was posted on dev tracker.